One of various known types of initiators is constituted by a pair of electrodes joined together via an insulator; a bridge wire connected with these two electrodes and adapted to generate heat when energized; and a casing that hermetically accommodates the bridge wire and an explosive able to detonate in response to heat generation of the bridge wire. This type of initiator is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) Nos. 2000-241099 and H11-301402.
In some cases, the components constituting the aforementioned conventional initiator, such as the electrodes and the insulator, receive high temperature and high pressure generated through detonation of the explosive. Therefore, the constitutive components (e.g., the electrodes and the insulator) are required to have high heat resistance and high pressure resistance. As an inflator for an airbag apparatus has been reduced in size, the pressure of a gas stored in the inflator has been increased. In accordance with this tendency, a load (high temperature and high pressure) applied to an initiator mounted on the inflator has been increased. Therefore, demand has arisen for enhancing the pressure resistance of the initiator.